Electronic package assemblies which utilize various organic substrates (e.g., printed circuit boards comprised of epoxy resin or the like material) having one or more electronic packages surface mounted thereon are known. Typically, such electronic packages include a relatively flat housing component having therein at least one semiconductor device (chip), which semiconductor device is in turn electrically connected to various conductive leads (e.g., copper) which project from designated sides of the housing. One such example is known in the art as a dual in-line package (DIP). Such packages in turn provide various functions (e.g., memory, logic) for the overall system which utilizes package assemblies of this type. Typically, the conductive leads which project from these packages are electrically coupled to respective conductor pads (e.g., copper) or the like which may form the circuitry on an upper surface of the organic substrate. As is known, various solder compositions may be used to provide individual connections between respective pairs of leads and conductors.
Recently, there have been developed electronic packages of relatively low profile which in turn include an insulative housing of relatively thin construction. Such packages are referred to in the art as TSOP's, TSOP standing for thin, small outline package. Such devices, being thin, occupy a minimum of height on the respective organic substrate and are further capable of being surface mounted to the substrate's respective circuitry (e.g., conductor pads) using known (e.g., soldering) techniques. These relatively new packages are known to include memory chips as the semiconductor devices thereof, but may provide other functions (e.g., logic) if desired. Significantly, these recently developed packages are able to provide such functioning while assuring a compact, low profile, thus representing a substantial savings in space for the final product utilizing same.
It has been discovered that when such packages are surface mounted on organic substrates (and particularly those of epoxy resin dielectric material) of relatively thick configuration (e.g., greater than about 0.050 inches thick), relatively significant stress is placed on the solder-lead joints, which stress can in turn adversely effect such joints, possibly causing separation thereof. Such resulting separation in turn may cause disconnection between the lead and solder, possibly rendering the package partially inoperative. Such stress is caused during operation of the package as a result of relatively substantial differences in the coefficients of thermal expansion of the relatively thick organic substrate and the coefficients of expansion of various other elements (e.g., the conductive leads, solder and package housing). Such differences are even more pronounced when thicker organic substrates (e.g., those including several conductive layers therein which function as signal, power or ground planes) are utilized. Thicker substrates are often desired in the computer industry in order to provide additional functioning within a singular member.
It is believed, therefore, that an electronic package assembly which permits the utilization of electronic packages such as those of the TSOP variety to be effectively utilized on organic substrates, and particularly those substrates of relatively thick dimensions, would constitute a significant advancement in the art.